High-speed Imaging Measurements Research Articles

Eulerian multi-fluid simulations of local liquid distribution in a bed packed with cylindrical particles

Packed bed reactors (PBRs) are extensively used in chemical process industries to perform solid-catalyzed gas–liquid reactions. Their performance is significantly influenced by liquid distribution which is a strong function of particle shape and size. In the present work, we simulated the steady-state local liquid distribution, pressure drop (ΔP/L), and overall liquid holdup (〈εL〉) for the beds packed with spherical and cylindrical particles using a three-dimensional (3D) Eulerian multifluid model and validated the predictions using corresponding high-speed imaging measurements performed in pseudo-2D packed beds. We showed that the Eulerian model with existing closures significantly underpredicts the liquid distribution for the bed randomly packed with cylindrical particles. To address this, we proposed a modification in existing mechanical dispersion force (F→D) model as a function of average particle orientation angle (θ). The modification significantly improved agreement between the predictions and the corresponding measurements. Using the modified model, we showed that the increased magnitude of F→D in the lateral direction leads to higher lateral liquid spreading for cylindrical particles as compared to that for the spherical particles. Importantly, the modified model also predicted the local liquid distribution and ΔP/L for beds packed manually with cylindrical particles oriented at different θ in a satisfactory agreement with the corresponding measurements. On increasing θ, the F→D in lateral direction (i.e., perpendicular to flow) as well as liquid–solid interaction force (F→LS) in axial direction (i.e., parallel to flow) found to increase significantly. As a result, the lateral liquid spreading as well as ΔP/L decrease substantially on increasing θ.

THz Radar Observations of Hydrometeors in a Spray Chamber

AbstractA THz radar, with its wide bandwidth, is capable of high‐resolution imaging down to the centimeter scale. In this study, a THz radar is applied to detect hydrometeors generated in a spray chamber. The observed backscattering signals show fluctuations at centimeter scales, indicating various hydrometeor distribution patterns along the radar beam. A co‐located High‐Speed Imaging (HSI) sensor is used to measure the Drop Size Distributions (DSD) in the spray chamber. The radar sampling beam is well aligned with the HSI probes, allowing an objective comparison between the remote sensing and in situ observations. In this study, the observed radar power is compared with the power estimated from the HSI measurements. Results show great consistency, with power difference smaller than 0.5 dB. This study demonstrates the feasibility and great potential of using a THz radar for ultra‐high‐resolution observations of clouds in a laboratory facility, and in the real atmosphere.

Fundamental Investigation of EDM Plasmas, Part I: A Comparison between Electric Discharges in Gaseous and Liquid Dielectric Media

Electric discharge machining (EDM) in liquid dielectric media is a well-stablished manufacturing process. Dry EDM (DEDM) has been proposed as an environmentally friendlier alternative to the EDM process in oil dielectric. The working principles of EDM and DEDM are based on interactions of electric discharge plasmas with electrodes materials, which is a poorly understood phenomenon. Therefore, optimization of EDM processes is still based on empirical methods and recipes. The investigation performed in the present work uses a collisional-radiative (CR) model for advanced optical emission spectroscopy interpretation of EDM plasmas performed in oil and air as dielectric media. This analysis is additionally supported by electrical parameter and high-speed imaging measurements. These applied plasma diagnostics allow, for the first time, a detailed comparison of EDM discharge plasmas in very different dielectric media. Emission spectra simulated by the CR model give indications on several EDM discharge properties, such as density of electrons, fraction of different ionic states and plasma composition. The emission spectra simulations indicate that EDM discharges performed in oil and air have very similar electron temperatures, while the electron densities are substantially different. In addition, the fraction of EDM plasma components is estimated quantitatively, indicating that plasmas in air are mostly composed of the electrodes materials, whereas EDM plasmas in oil are dominated by species originated from the dielectric medium.

Crack initiation behavior in single crystalline silicon

In this article, we report special fracture initiation behavior of (110) cleavage in silicon single crystal. It is found that the static energy release rate always exceeds the material toughness upon crack initiation. According to high-speed imaging measurements and fractographies, it is found that the crack has an important initial velocity, i.e. up to 3000m/s, and then reaches the steady-state propagation regime very quickly. The experimentally revealed initial crack velocity is in good agreement with estimation from the energy flux at crack initiation.

Sequential deposition of overlapping droplets to form a liquid line

AbstractMicrodroplet deposition is a technology that spans applications from tissue engineering to microelectronics. Our new high-speed imaging measurements reveal how sequential linear deposition of overlapping droplets on flat uniform substrates leads to striking non-uniform morphologies for moderate contact angles. We develop a simple physical model, which for the first time captures the post-impact dynamics drop-by-drop: surface-tension drives liquid redistribution, contact-angle hysteresis underlies initial non-uniformity, while viscous effects cause subsequent periodic variations.

Experimental and Numerical Investigation of Particle Kinematics in Shotcrete

AbstractThe intent of this paper is to identify the basic physical laws governing particle kinematics in a shotcrete spray. This paper presents a governing equation based on Newton’s second law where nozzle and airflow characteristics, and particle features are used to predict impact velocity of the material exiting the nozzle. Experimental values obtained using high-speed imaging measurements on marbles and aggregate particles correlate well with the results of numerical simulations on a simplified spraying system. With the controlling parameters of particle kinematics fully understood, the analysis of the governing equations offers essential elements for nozzle optimization and new mix design investigations. This paper also addresses the necessity of broadening the investigation to the entire spray of particles exiting the nozzle for a complete understanding of the spraying process on placement mechanisms at a process scale.

High-Speed Image Measurement Technology and its Application under Toner Drop Impact Test

A transport package cushioning property evaluation test system is established to achieve the goal of high-precision, real-time, non-contact, and full-field measurement. It consists of a shock testing machine, a shock measuring instrument and a high-speed image acquisition and processing system. High-speed imaging measurement techniques and digital image processing method are used to make a comprehensive assessment on the cushioning properties of air-cushion package. In this paper, the developed system was used to measure the drop shock responses of the toner and air cushion deformation under drop impact test.

Effect of expansion chamber geometry on atomization and spray dispersion characters of a flashing mixture containing inerts. Part II: High speed imaging measurements

A breath activated, pressurized metered dose inhaler (pMDI) device (Oxette®) has been developed to replace the traditional cigarette. In this paper, internal and external spray characters are measured by high speed imaging along with sizing the residual droplets at the distance from the discharge orifice where the human oropharynx locates. Two different formulations with 95% and 98% mass fraction of HFA 134a and two prototype cigarette alternatives with different expansion chamber volumes have been analyzed. The internal and external flows issuing from early stage prototype Oxette® are discussed along with boiling and evaporation phenomena. The expansion and entrainment regions of the jet are observed and discussed with comparison to the turbulent round jet of a single phase. From the visualizations of internal flows in the earlier design, a small expansion chamber can hardly generate small bubbles, which is difficult to produce fine sprays. The larger the expansion chamber volume, the more room for the propellant evaporation, recirculation, bubble generation and growth, all of which produces finer sprays. Therefore the later prototype of Oxette® 2 made a significant improvement to produce fine sprays and facilitated development of the cigarette alternative. Furthermore, the characters of the spray generated by Oxette® are compared to that issuing from a pMDI by previous researchers, where the residual MMD is larger than that of a pMDI, because the Oxette® has a smaller expansion chamber and the geometry provides less opportunity for the recirculation due to restrictions of the design space. Although the formulation with higher mass fraction of HFA 134a can generate smaller droplets, it cannot produce steady puffs with relatively low mass flow rate.

Flow Fields and Acoustics in a Unilateral Scarred Vocal Fold Model

From prior work in an excised canine larynx model, it has been shown that intraglottal vortices form between the vocal folds during the latter part of closing. It has also been shown that the vortices generate a negative pressure between the folds, producing a suction force that causes sudden, rapid closing of the folds. This rapid closing will produce increased loudness and increased higher harmonics. We used a unilateral scarred excised canine larynx model to determine whether the intraglottal vortices and resulting acoustics were changed, compared to those of normal larynges. Acoustic, flow field, and high-speed imaging measurements from 5 normal and 5 unilaterally scarred canine larynges are presented in this report. Scarring was produced by complete resection of the vocal fold mucosa and superficial layer of the lamina propria on the right vocal fold only. Two months later, these dogs were painlessly sacrificed, and testing was done on the excised larynges during phonation. High-speed video imaging was then used to measure vocal fold displacement during different phases. Particle image velocimetry and acoustic measurements were used to describe possible acoustic effects of the vortices. A higher phonation threshold was required to excite the motion of the vocal fold in scarred larynges. As the subglottal pressure increased, the strength of the vortices and the higher harmonics both consistently increased. However, it was seen that increasing the maximum displacement of the scarred fold did not consistently increase the higher harmonics. The improvements that result from increasing subglottal pressure may be due to a combination of increasing the strength of the intraglottal vortices and increasing the maximum displacement of the vocal fold; however, the data in this study suggest that the vortices play a much more important role. The current study indicates that higher subglottal pressures may excite higher harmonics and improve loudness for patients with unilateral vocal fold scarring. This finding implies that therapies that raise the subglottal pressure may be helpful in improving voice quality.